This invention relates to total knee replacement or arthroplasty and particularly to an alignment apparatus and method for aligning a resection guide used in resecting the tibial plateau.
In total knee replacement or arthroplasty, the proximal surface of the tibia is removed or resetted and an implant affixed over the resected surface. The implant includes artificial articulating surfaces to replace the natural articulating surfaces which have been removed. The resection of the proximal surfaces of the tibia must leave a surface having a specific posterior slope and varus/valgus angle that are unique to every patient. Also the depth of the cut must be specifically tailored for the thickness of the implant in order to properly position the artificial articulating surfaces.
Due to the critical nature of the cut required through the tibial plateau, a saw guide block or resection guide is preferably fixed to the tibia and used to guide a saw blade in making the cut. The resection guide includes a planar guide surface that guides the saw blade in the appropriate plane to produce the desired resected surface. The resection guide itself must be aligned with its planar guide surface in the plane necessary to provide the desired cut, and alignment devices have been developed to align the resection guide with respect to the surgically exposed tibia. Using the alignment instrument, the resection guide is aligned primarily to match natural landmarks of the tibial plateau and lower leg.
The alignment devices include means for adjusting the posterior/anterior slope of the resection guide, the depth of the resection guide's guide surface below the top of the tibia, and the varus/valgus or lateral/medial slope. Tibial resection guide alignment devices fall into two broad categories, extramedullary mounted devices and intramedullary mounted devices. The extramedullary devices are connected outside the patient's tibia while the intramedullary alignment devices include an intramedullary rod that is positioned down the central canal of the tibia and the alignment mechanism suspended from the rod. In either type of alignment device, the resection guide was first attached to the device, the device was connected to the patient, and then the alignment device was operated to provide the desired alignment. Once the resection guide was aligned, it was temporarily fixed in place on the anterior side of the tibia and the alignment device removed to allow the cutting or resection operation.
An intramedullary or extramedullary mount is generally a matter of preference for the particular surgeon. Prior alignment guides were restricted to one type of mount, either intramedullary or extramedullary. Therefore, to meet surgeon preference, two sets of tools had to be available. Furthermore, the prior intramedullary mounted alignment guides did not provide fine adjustments for cutting depth and slope.